Each standard process alarm (except for fail) uses two parameters with the following name relationship:
alarm_ACT - One (1) when true (in alarm)
alarm_LIM - Associated limit value
For example, the HI alarm shown in the preceding check box has the following parameters:
HI_ACT - HI alarm state parameter (true = in alarm)
HI_LIM - HI alarm limit parameter (PV > HI_LIM = alarm)
All standard alarms use a calculation according to the following form:
HI_ACT is true if PV > Alarm Limit
The system sends the alarm to DeltaV Operate when the HI_ACT parameter becomes true (HI_ACT is true when HI_LIM exceeds the limit value). All alarm calculations (that is, *_ACT) are basically true/false conditions, where the true condition indicates that the alarm is active. All alarms (for example, HI_ACT in the preceding discussion) display the configured alarm word (for example, High) in DeltaV Operate when there is an alarm.